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Europa's Ice May Be Miles Thick
serutan writes "Space.com has an article detailing recent measurements of the shell of ice covering what is believed to be an enormously deep ocean on Europa, which could harbor life. The thickness of the ice -- many times the previous estimate -- poses a major obstacle to sending a lander that would burrow down through it to the water. [Seems like if they could make the probe kinda warm it would eventually sink through any amount of ice.]"
Seems like if they could make the probe kinda warm it would eventually sink through any amount of ice.
That's a bit of an understatement. Let's do a quick calculation, shall we?
The article says that the ice is at least 19km (11 miles) thick. Let's assume we can somehow magically make our probe fit into the volume of a square foot or 30cm per side. That means we have about 1700 square meters of ice to melt, which is around 2e6 kilograms.
Europa has no real atmosphere, the pressure at the surface is around 1e-11 bar (1e-6 Pa) -- i.e. almost nothing. So the ice would most certainly vaporize rather than melt, and at a temperature lower than 0C. See this neat phase diagram of water. As we go down farther the pressure will necessarily increase, but I don't feel like calculating it exactly. Based on the phase diagram I'll use 200K as the approximate transistion temperature. It's close enough to be within an order of magnitude of correct.
The surface temperature of Europa is approx -260 dF (111 Kelvin), so to raise it to 200K results in a temperature difference of 89K. The specific heat of ice is around 2e3 J/(kg*K). That means our task will require about 3.5e11 Joules of energy. Let's say we let this process take 100 years at a steady rate. This comes to about 111 Watts. Suddenly "kinda warm" really doesn't cut it.
When you have a self contained source of power that can supply 111 W constantly for 100 years and fit into a square foot of volume, please let me know. Surely, you would have solved our energy crisis by now.
PS - Solar panels are pretty much useless after you get farther from the sun than Mars. That's why probes like Cassini needs radio-isotope thermo-electric generators.